1. Field of the Invention
The present invention relates to a piston-integrated seal which is used in a hydraulic clutch of an automatic transmission in a vehicle.
2. Description of the Conventional Art
FIG. 4 shows a hydraulic clutch which employs a conventional piston-integrated seal, and FIG. 5 shows an outline structure of the conventional piston-integrated seal.
First of all, in the hydraulic clutch shown in FIG. 4, reference numeral 1 denotes an annular clutch cylinder which rotates together with a drive shaft (not shown), reference numeral 2 denotes a clutch piston which is arranged within the clutch cylinder 1 so as to be movable in an axial direction, and defines a hydraulic chamber S1 between the clutch piston and an end plate portion 11 of the clutch cylinder 1, reference numeral 3 denotes a spring holder which is arranged in a space S2 in an opposite side to the hydraulic chamber S1 as seen from the clutch piston 2 and is locked its inner diameter to an inner tube portion 13 of the clutch cylinder 1, reference numeral 4 denotes a return spring which is interposed between the clutch piston 2 and the spring holder 3 in an appropriately compressed state, and reference numeral 5 denotes a multiple disc clutch constructed by a plurality of drive plates 51 which are locked to the clutch cylinder 1 side in a circumferential direction under a movable state in an axial direction, and a plurality of driven plates 52 which are locked to a clutch hub 53 provided in a driven shaft side in a circumferential direction under a movable state in an axial direction.
This kind of hydraulic clutch is structured such that the piston 2 displaces in an axial direction within the clutch cylinder 1 by applying a hydraulic pressure to the hydraulic chamber S1 via a pressure guide port 14 which is provided in the inner tube portion 13 of the clutch cylinder 1 or releasing the hydraulic pressure, thereby friction fastening the drive plate 51 and the driven plate 52 of the multiple disc clutch 5 or canceling the friction fastening so as to carry out a clutch connection and disconnection motion.
A packing such as an O-ring has been conventionally used as a seal means for inner and outer peripheries of the clutch piston 2, however, the clutch piston 2 is desired to be lowered its friction in order to achieve an improvement of fuel consumption and a reduction of shift shock (a shock generated at the friction fastening time of the clutch). In recent years, a piston-integrated seal 100 having seal lips 101 and 101 has been a mainstream, the seal lips 101 and 101 being slidably brought into close contact with the outer tube portion 12 and the inner tube portion 13 of the clutch cylinder 1 while being directed to the hydraulic chamber S1 side. In other words, the piston-integrated seal 100 is integrally formed in the clutch piston 2 by a rubber-like elastic material (a rubber material or a synthetic resin material having a rubber-like elasticity) (refer, for example, to Japanese Unexamined Patent Publication No. 2001-241467).
As shown in FIG. 5, the seal lip 101 is generally structured such that an angle α of an inclined surface closer to the hydraulic chamber S1 side than the seal edge portion where a contact pressure P (an interference L) in relation to the other sliding surface shown by a two-dot chain line in the drawing is the greatest is larger than an angle β of an inclined surface in an opposite side, and a length Ha in an axial direction from the seal edge portion to the root portion in the opposite side to the hydraulic chamber S1 is comparatively long.